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Tropical Storm Harvey Forecast Discussion Number 7
2017-08-19 04:33:57| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Fri Aug 18 2017 000 WTNT44 KNHC 190233 TCDAT4 Tropical Storm Harvey Discussion Number 7 NWS National Hurricane Center Miami FL AL092017 1100 PM AST Fri Aug 18 2017 Microwave and conventional geostationary satellite images indicate that Harvey's center is still displaced to the east of a persistent cluster of deep convection due to about 15 kt of northeasterly shear. With no notable changes in the cyclone's structure since the last advisory, the maximum wind estimate remains 35 kt, which is in line with the latest Dvorak CI numbers. Recent microwave fixes suggest that Harvey's center may have slowed down or wobbled northward temporarily, and the 12-hour motion estimate is a slightly slower 275/16 kt. A low- to mid-level ridge extending across the western Atlantic should keep Harvey on a swift westward course across the Caribbean Sea for the next 48 hours. Once Harvey moves into the northwestern Caribbean Sea by 72 hours, it will reach the western edge of the ridge, and it will likely slow down and gain some latitude due to a cut-off low over the northwestern Gulf of Mexico. Although the track guidance envelope has shifted slightly northward on this cycle, especially around the 72-hour period, there are no significant changes from six hours ago. Northeasterly or northerly shear is forecast to continue for the next 36 hours or so, which should prevent significant strengthening while Harvey moves westward across the eastern and central Caribbean Sea. By 48 hours, the vertical shear over the cyclone drops drastically, but the system's fast motion could still limit the amount of intensification that will occur. The best opportunity for strengthening would likely be around day 3 when Harvey begins to slow down as it approaches Belize and the Yucatan Peninsula. The updated NHC intensity forecast is the same as the previous one during the first 48 hours, and it was nudged a little lower at 72 hours to fall closer to the HFIP Corrected Consensus (HCCA) model and the ICON intensity consensus. A lot of uncertainty remains, however, since models like SHIPS and HWRF bring Harvey near or to hurricane intensity before it reaches land while the GFS and ECMWF continue to weaken the circulation while it moves across the Caribbean Sea. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 13.7N 64.1W 35 KT 40 MPH 12H 19/1200Z 14.0N 66.8W 35 KT 40 MPH 24H 20/0000Z 14.3N 70.4W 40 KT 45 MPH 36H 20/1200Z 14.5N 74.3W 40 KT 45 MPH 48H 21/0000Z 14.8N 78.1W 45 KT 50 MPH 72H 22/0000Z 16.5N 84.7W 55 KT 65 MPH 96H 23/0000Z 18.0N 89.5W 45 KT 50 MPH...INLAND 120H 24/0000Z 19.0N 92.5W 40 KT 45 MPH...OVER WATER $$ Forecaster Berg
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